Many devices such as electronic instruments, lasers, etc, require a calibration before they can operate properly. Calibration involves correlating the device's input to its output; in other words, for each desired output calibration establishes the input values that produce that output. At its simplest, for example in a device having a single input, calibrating the device is a relatively simple matter of correlating output to input. In more complex devices having multiple inputs, however, there may be multiple combinations of inputs that produce the same output; in these cases, some form of optimization can be performed to determine which combination of inputs best produces the desired output based on some figure of merit. For instance, one may want the combination of inputs that produces the desired output using the minimum amount of power. Using a tunable laser as an example, proper tuning of the laser requires that various components within the laser be maintained at specified temperature. In most devices the temperature is not controlled directly. Instead, the temperature is the result of applying some other characteristic, such as an electrical current, to the component. A calibration must be performed to determine what electrical current and/or voltage will correspond to a given temperature, and what wavelength results from a given temperature.
In most cases—especially those where there is some optimization in the calibration—the calibration can be expensive and time consuming, and may require very specialized and expensive equipment. The result of a calibration is usually a set of calibration data, also known as a “calibration table” or a “calibration matrix.” The calibration table or matrix usually tabulates or otherwise sets forth the desired outputs along with the inputs that produce those outputs. The data can be presented in the table or matrix in raw form or in some alternative presentation, such as a polynomial, spline, or other representation of the output as a function of the input variables. For simple devices the calibration data can comprise only a small amount of data, but for more complex devices such as a tunable laser the set of calibration data will be substantially larger.
Some devices require a unique set of calibration data for each unit. For example, the performance of some devices, such as tunable lasers, is extremely sensitive to manufacturing tolerances; in such cases, no single calibration will work properly for every single unit of the device, because every unit will be different due to differences caused by the buildup of manufacturing tolerances. For such devices, an individual and unique calibration must be performed for every single unit produced.
In many, if not most, devices, the calibration data is stored not in the device itself, but rather is stored electronically in a controller. In some devices, the controller is part of the device itself, but in others-particularly in miniaturized devices that have no space for an internal controller-the controller is a separate unit. When the calibration data is stored in a controller separate from the device the calibration data becomes associated with the controller, rather than with the device. This presents a pair of problems: first, in some cases the device may be sold without an attached controller, so that the customer may choose a controller that best meets their particular use of the device. Second, whether or not the controller is sold with the device, if the controller is ever damaged or replaced, the calibration data specific to the device to which the controller was coupled will disappear. For example, if the controller is damaged by a power surge, the user could simply swap in a new controller. The new controller, however, would not have the calibration data stored on it and, because the original controller was damaged, the calibration data could not be recovered from it. Thus, the user would have to re-calibrate the device each time a new controller is installed. A user may not want to invest the substantial amount of time necessary for calibration, and may also not want to invest in the expensive and sometimes extensive instrumentation needed. In this case, the user's only recourse would be to return the device to the manufacturer for recalibration, which would result in significant downtime for the user as well as significant expense for both the user and the manufacturer.